Mouse amniotic fluid (MAF) has been shown to be suppressive, both in vivo and in vitro, for antibody synthesis and for certain cell- mediated reactions (mitogen stimulation and mixed lymphocyte reactions). The suppressive factor has been isolated from MAF and identified as alpha-fetoprotein (AFP). We propose to study the chemical properties and antigenic cross-reactions of AFP's from several species. Attempts will be made to determine the primary structure of those regions of the molecule responsible for binding and inactivation. The type of cell(s) involved will be studied by binding AFP to isolated preparations of T cells, B cells and macrophages. I 125 AFP and the fluorescent antibody technique will be used to study binding. A Marbrook double-chamber technique will also be employed to attempt to determine which cell type(s) are suppressed by AFP. A possible role for AFP in the immunosuppression reported in experimental mouse and human tumors will be investigated. AFP will be measured by radioimmunoassay in serum and ascitic fluid in mouse tumors (sarcoma I, EL-4, mastocytoma, Ehrlich ascites tumor, and plasmacytomas) and in certain human tumors. Using the fluorescent antibody technique, circulating lymphocytes will be examined for bound AFP. AFP synthesis by mouse and human tumor tissue will be studied using in vitro culture with C 14 leucine and precipitation with anti-AFP antisera. The effect of AFP on in vitro tumor cell cytotoxicity , B cell-mediated cytotoxicity and the release of MIF by mitogens and antigens will be investigated. The effect of AFP administered in vivo on the growth of experimental mouse tumors (including carcinogen-induced) will be studied. Lymphocytes from patients with malignancies who show evidence of suppression by mitogen stimulation will be cultured in vitro for 6 days in order to determine whether suppression (as determined by mitogen and MLR) is affected and whether suppressive factors (AFP, immunoglobulin or others) can be identified in culture supernates.